In vivo studies performed in our laboratories have demonstrated that misonidazole (MISO) and other radiation sensitizers can enchance the anti-tumor effectiveness of nitrosourea chemotherapeutic agents and that the magnitude of enhancement is directly correlated with the carbamoylating potential of the individual nitrosoureas. In other envrionmental systems carbamoylation has been related to DNA repair inhibition and synergism with other DNA damaging agents such as ionizing radiation. Therefore, in the current application we propose to test the hypothesis that carbamoylation and its associated repair inhibition are correlated with the magnitude of response enhancement produced when nitrosoureas are combined with radiation sensitizers for the treatment of EMT6 and KHT tumor cells in vitro. This relationship will be evaluated using monolayer cultures and multicell spheroids in vitro, making it possible to control and minimize many variables which presently complicate interpretation of our in vivo data. Experiments have been designed to examine the mechanism(s) of interaction responsible for the enhanced anti-tumor effectiveness of these combinations by determining how the interaction with MISO is influenced by: (1) changes in the chemical structure, and thereby the carbamoylating and alkylating properties of the nitrosourea; (2) the cellular environment at the time of exposure (hypoxic vs. oxic; monolayer vs. spheroid); and (3) the proliferative status of the cells at the time of exposure (plateu vs. exponential cultures). These studies will provide basic information which may (1) provide valuable insight into the biophysical nature of the interaction between the nitrosoureas and radiation sensitizers, (2) indicate whether hypoxia is required to produce enhancement when sensitizers are combined with anti-tumor drugs, (3) establish a rational process for selecting those agents which, based on their chemical activities, possess the greatest potential for enhanced tumor response when combined with sensitizers, and (4) guide the design of new agents that possess the desired biological activities required to maximize the enhancement produced in combination with sensitizers and other similarly acting drugs.